Hydrothermal liquefaction (HTL) of biomass is a strategic process to convert renewable feedstocks into a biofuel (i.e. biocrude). Despite their importance, the research has not deeply investigated the fate of aqueous side-streams, that may contain up to 30% of the carbon present in the original biomass feed. Aqueous phase reforming (APR) may be a key process to convert the organics into a gas phase rich in hydrogen. In turn, it may be used to perform the upgrade of the biocrude, reducing its oxygen content (Figure 1, left). It is estimated that in the hydrothermal processes the cost of the waste water disposal is second only to the feedstock costs. Moreover, the main source of the hydrogen used in a biorefinery still comes from fossil nature, in big centralized plants. Valorizing the aqueous by-products aiming to produce the required hydrogen of a biorefinery (i.e. for deoxygenation reactions) would solve two critical issues connected with their development. In the present work, seventeen representative compounds, several synthetic mixtures and real liquid phase coming from the HTL of lignin have been tested at different reaction temperatures (230-270 °C) with 5% Pt/Al2O3 and 5% Pt/C catalysts. The intrinsic tendency toward hydrogen production of several molecules belonging to different class of compounds (carboxylic and bicarboxylic acids, alcohols, hydroxyacids, ketones, aromatics) has been investigated. Together with the gas phase, a thorough characterization of the liquid phase was performed to determine key intermediates/by-products present at the end of the reaction. In Figure 1 (right) the hydrogen yield at 270 °C of the seventeen representative compounds is reported. Subsequently, focus is given to the study of real HTL-derived streams, which raised key issues related to the activity and -more critically- to the stability of the catalyst because of the presence of the aromatic compounds. Mitigating this deactivation was the object of investigation, through the tuning of the pre-treatment of the aqeuous phase, also in relation to the desired Carbon yield in the biocrude.

Aqueous phase reforming of the waste water derived from lignin hydrothermal liquefaction: From the simplicity of model compounds to the complexity of real streams

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.